What should be checked if the burner fails to ignite?

When a burner fails to ignite, the power supply to the fan is a critical factor to check first. The fan is responsible for supplying air to the combustion chamber, which is essential for the ignition process. If the power supply to the fan is disrupted or inadequate, the fan will not operate, leading to insufficient airflow. This absence of airflow means there is not enough oxygen to support the combustion of the oil, resulting in ignition failure.

In contrast, while oil viscosity can affect the efficiency of the burner, it does not directly relate to the immediate factors preventing ignition. Similarly, the age of the burner might indicate potential wear or need for replacement but does not directly impede the ignition process. Lastly, checking oil color is relevant for diagnosing oil quality, but it does not provide direct insight into why the burner is failing to ignite at that moment. Thus, ensuring that the power supply to the fan is functioning correctly addresses an immediate and fundamental requirement for the burner to operate effectively.